XXX still in progress
In reference-typed languages, the reference to storage has a type; and the storage always exists with data in it, albeit the data may be nonsensical or, for languages with null references, "not pointing to an object."
In value-typed languages, references are of type top type ⊤, inhabited by
all values of all types, or effectively untyped. These languages may or may
not have "null" references; interpreted languages such as Lisp, Python and
Ruby don't because nil and None are actual objects, not lack of an
object.